This invention relates to a transmission power control unit, in particular, to a transmission power control unit for use in a transmitting apparatus for transmitting transmission data with the transmission data multiplexed, such as a radio base station apparatus for use in a code division multiple access (CDMA) communication system.
For example, in a cellular mobile communication system such as the code division multiple access (CDMA) communication system, a service area is divided into a plurality of units called cells in each of which a radio base station apparatus is installed, and the radio base station apparatus carries out transmission and reception with mobile station apparatuses lying the cell in question.
In such a radio base station apparatus, it is necessary to accurately control transmission power so that a transmission signal covers within its own cell without affecting other cells.
Particularly, in the radio base station apparatus for transmitting a plurality of channels with the channels multiplexed, the following problems arise when all of the channels multiplexed are transmitted at equal transmission power. That is, interference occurs in mobile station apparatuses in the vicinity of the radio base station apparatus due to too strong electric wave and it is possible to normally receive the transmission signal in mobile station apparatuses away from the radio base station apparatus due to too weak electric wave. In addition, inasmuch as the radio base station apparatus naturally has a limited transmission power enable to output, it is necessary to assign the limited transmission power to each mobile station apparatus or each channel. Under the circumstances, it is necessary for the radio base station apparatus to adjust the transmission power each channel in accordance with factors such as a distance between each mobile station apparatus and the radio base station apparatus in question.
In addition, in the CDMA communication system, when the channels to be multiplexed increase, the whole transmission power increases. As a result, it is possible to insure a lot of usable channels by accurately controlling the transmission power for each channel at the necessary lowest limit in a plurality of channels multiplexed in consideration of near-far problem. Accordingly, it is desirable to accurately carry out transmission power control for each channel.
In a transmitting apparatus carrying out such a multiplexing, a conventional transmission power control unit necessitates a digital-to-analog converter for converting a digital signal indicative of a digital value into an analog signal indicative of an analog value. This is because to adjust an output of a power amplifier demands the analog value although a control value for carrying out the power control is given by the digital value.
Incidentally, the above-mentioned transmission power control is carried out on the premise that the digital-to-analog converter in the transmission power control unit operates ideally. However, actually, a variation amount of the digital signal and a variation amount of an analog signal to be outputted are not perfectly coincident with each other and the digital-to-analog converter may have a demolished linearity. In addition, the digital-to-analog converter is supplied with a reference voltage or a power supply voltage which may vary. As a result, the conventional transmission power control unit is disadvantageous in that it is impossible to obtain a correct analog amount corresponding to the digital value using the digital-to-analog converter and it is difficult to actually carry out correct transmission power control.
In addition, the conventional transmission power control unit is disadvantageous in that precision in the power control degrades due to the influence of variation of temperature and secular change in a part of analog circuits in the next stage of the digital-to-analog converter.
Furthermore, it is necessary for the CDMA communication system to carry out control of the transmission power each channel as described above. However, the conventional transmission power control unit is disadvantageous in that it is impossible to detect the transmission power each channel that is actually transmitted because each channel is multiplexed on the same radio carrier.
Various CDMA communication systems related to the present invention are already known. An example is disclosed in U.S. Pat. No. 5,737,327 which is issued to Ling et al. on Apr. 7, 1998 and which has a title of xe2x80x9cMethod and apparatus for demodulation and power control bit detection in a spread spectrum communication system.xe2x80x9d According to Ling et al., a receiver circuit receives a spread spectrum communication signal, such as a DS-CDMA signal, including a pilot channel and including a power control designator. The spread spectrum communication signal is despread and decoded. The pilot symbols on the pilot channel are provided to a channel estimator for estimating the channel phase and channel gain of the communication channel. This estimate is provided to a demodulator for demodulating the traffic channel symbols. The pilot symbols are provided to another channel estimator for estimating channel phase and channel gain for the power control designator. This estimate is provided another demodulator for demodulating the power control designator. The traffic channel symbols are delayed a predetermined time in a delay element before demodulating. The power control designator is delayed a short time or not at all in a short delay element before demodulation.
Japanese Unexamined Patent Publication of Tokkai No. Hei 7-235,913 or JP-A 7-235913 discloses a spread spectrum communication equipment and signal intensity detecting device which are capable of informing a user a stable talking standard by measuring the signal power intensity of a base station in a spread spectrum communication mode. According to JP-A 7-235913, in a spread spectrum communication equipment, the gain control signal sent from a detector of an automatic gain control (AGC) circuit is converted into the electric power serving as the signal intensity by another detector and sent to a multiplier. The electric power of the desired pilot channel of a base station is detected out of the output signal received from the AGC circuit by a spread code detector and sent to the multiplier. The multiplier calculates the signal intensity of the desired base station based on the received electric power and sends it to a display part. Then the display part shows the signal intensity.
Japanese Unexamined Patent Publication of Tokkai No. Hei 8-8,877 or JP-A 8-008877 discloses a spread spectrum radio communication system and radio communication equipment used in the system which are capable of eliminating the need of complicated numerical arithmetic operation in a mobile station and the transmission of surrounding signal, of improving communication efficiency, of miniaturizing and lightening a mobile station equipment, and of lowering power consumption. According to JP-A 8-008877, in a base station, the radio transmission characteristics of a forward link are estimated by a parameter estimation part based on the reception state of radio signals arriving from the mobile station through a reverse link, RAKE control information to be set in the RAKE receiver of the mobile station is generated based on the estimated result and the mobile station is informed of the RAKE control information. On the other hand, in the mobile station, the RAKE control information is extracted in a RAKE control information extraction part and a tap coefficient is initially set in the transversal filter of the RAKE receiver based on the RAKE control information.
Japanese Unexamined Patent Publication of Tokkai No. Hei 10-41,919 or JP-A 10-041919 discloses a CDMA system multiplex transmitter which is capable of attaining reception always stably from all channels by inserting a power measurement power control code to a spread code of each channel measuring transmission power of each channel in an output of a radio section so as to control the transmission power of each channel to be arranged as a prescribed value. According to JP-A 10-041919, a power control section uses transmission data spread and outputted from a channel section as a first input and uses a power control signal outputted from a despread section as a second input to select and correct amplitude data and provide an output. A frequency conversion section receiving a power control output converts the signal into a prescribed frequency band and provides an output. The despread section uses the frequency-converted signal as a first input and uses the power control code generated by a power control code generating section as a second input to conduct despread processing thereby detecting an instantaneous power of each channel. The despread processing is conducted in the order of channels according to a clock received from a timing control section and a power control signal is outputted to each power control section.
Japanese Unexamined Patent Publication of Tokkai No. Hei 9-284,212 or JP-A 9-284212 discloses a spread spectrum communication system which is capable of reducing interference onto its own station adjacent cells and of increasing a subscriber capacity while eliminating a nearfar problem by adjusting a process gain depending on a distance of a mobile station from a center of a cell. According to JP-A 9-284212, an information transmission section of a transmission section applies primary modulation to information data consisting of a voice signal, data and an image or the like based on a data clock from a data clock generator to be information data having a prescribed data transmission speed and the resulting data are given to a spread modulation section. Furthermore, a PN clock from a PN clock generator is given to a PN generator, from which a PN signal with a prescribed spread speed is generated and given to the spread modulation section. Then a distance from a base station is estimated, each mobile station adjusts a spread speed based on the estimated distance. The spread speed is adjusted by controlling a clock frequency from the PN clock generator to be supplied to the PN generator.
It is therefore an object of the present invention to provide a transmission power control circuit which is capable of accurately carrying out transmission power control each channel.
Other objects of this invention will become clear as the description proceeds.
According to a first aspect of this invention, a transmission power control method controls transmission power in a digital signal. The transmission power control method comprises the steps of converting the digital signal into an analog signal by a digital-to-analog converter, of power amplifying the analog signal into a power-amplified signal by a power amplifier, of extracting a part of the power-amplified signal as an extracted signal, and of adjusting the digital signal using the extracted signal.
According to a second aspect of this invention, a transmission power control method controls transmission power in a transmission amplitude datum. The transmission power control method comprises the steps of spreading the transmission amplitude datum into a spread datum, of converting the spread datum into a transmission signal, of extracting a part of the transmission signal as an extracted signal, and of adjusting the transmission amplitude datum on the basis of the extracted signal.
According to a third aspect of this invention, a transmission power control method controls transmission power in a transmission amplitude datum. The transmission power control method comprises the steps of spreading the transmission amplitude datum into a spread datum, of converting the spread datum into a transmission signal, of extracting a part of the transmission signal as an extracted signal, of despreading the extracted signal to obtain transmission power in the transmission amplitude datum, and of adjusting the transmission amplitude datum on the basis of the obtained transmission power.
According to a fourth aspect of this invention, a transmission power control method controls transmission power in a transmitting apparatus for transmitting first through N-th transmission amplitude data for first through N-th channels with the first through the N-th transmission amplitude data multiplexed, where N represents a positive integer which is not less than two. The transmission power control method comprises the steps of spreading the first through the N-th transmission amplitude data into first through N-th spread data, respectively, of multiplexing the first through the N-th spread data into a multiplexed amplitude datum, of converting the multiplexed amplitude datum into a transmission signal, of extracting a part of the transmission signal as an extracted signal, of despreading the extracted signal to produce first through N-th detected signals indicative of transmission power for the first through the N-th channels, respectively, and of adjusting the first through the N-th transmission amplitude data on the basis of the first through the N-th detected signals, respectively.
According to a fifth aspect of this invention, a transmission power control unit is for use in a transmitting apparatus for transmitting first through N-th power-controlled transmission amplitude data for first through N-th channels with the first through the N-th power-controlled transmission amplitude data multiplexed, where N represents a positive integer which is not less than two. The transmission power control unit comprises first through N-th power control amount correctors supplied with the first through the N-th power-controlled transmission amplitude data, respectively. The first through the N-th power control amount correctors carry out, on the basis of first through N-th detected signals, correction of first through N-th power control amounts on the first through the N-th power-controlled transmission amplitude data to produce first through N-th corrected data, respectively. A power control correction code generator generates a power control correction code for detection of transmission power. Connected to the first through the N-th power control amount correctors, respectively, and to the power control correction code generator in common, first through N-th spreading sections carry out first through N-th spread processings on the first through the N-th corrected data using first through N-th replaced spreading codes into which respective parts of first through N-th spreading codes assigned with the first through the N-th channels are replaced with the power control correction code, respectively. The first through the N-th spreading section produce first through N-th spread data. Connected to the first through the N-th spreading sections, a multiplexer multiplexes the first through the N-th spread data by summing up the first through the N-th spread data. The multiplexer produces a multiplexed amplitude datum. Connected to the multiplexer, a digital-to-analog converter converts the multiplexed amplitude datum into an analog signal having an analog value corresponding to the multiplexed amplitude datum. Connected to the digital-to-analog converter, a radio section carries out modulation, frequency conversion, and power amplification on the analog signal to produce a transmission signal. Connected to the radio section, an extracting arrangement extracts a part from the transmission signal as an extracted signal. Connected to the extracting arrangement, a frequency converter converts the extracted signal into a frequency-converted signal having a frequency which enables the frequency-converted signal to digitally process. Connected to the frequency converter, the power control correction code generator, and the first through the N-th power control amount correctors, a despreading section carries out a despread processing on the frequency-converted signal to detect first through N-th momentary transmission power for the first through the N-th channels. The despreading section supplies the first through the N-th power control amount correctors with the first through the N-th detected signals indicative of the first and the N-th momentary transmission power, respectively. Connected to the despreading section and the first through the N-th spreading sections, a timing controller generates a clock signal for synchronizing the despreading section and the first through the N-th spreading sections. The timing controller supplies the despreading section with the clock signal. The timing controller supplies the first through the N-th spreading sections with first through N-th timing signals, respectively.
According to a sixth aspect of this invention, a transmission power control method controls transmission power in a radio base station apparatus for use in a code division multiple access (CDMA) system. The transmission power control method comprises the steps of replacing a part of a spreading code assigned with each channel with a power control correction code having orthogonality to produce a replaced spreading code, the power control correction code having a code length which is extremely shorter than that of the spreading code, of spreading a spectrum of a transmission datum using the replaced spreading code to produce a transmission signal, of despreading the transmission signal using the power control correction code to measure transmission power in the transmission datum each channel, and of carrying out, on the basis of measured transmission power, transmission power control for the transmission datum each channel.